1. Field Of The Invention
This invention generally concerns vacuum systems for removing cut or abraded particles from a working surface and more particularly concerns a vacuum system for removing water and swarf from the cutting path of a pavement grooving machine.
2. Description Of Prior Developments
In the road surfacing industry it is frequently necessary to increase tire traction upon a paved roadway surface. A common solution is to cut a series of grooves into the pavement surface with a groove cutting device having a ganged saw blade assembly. Up to several dozen diamond grooving blades may be mounted upon a common shaft and driven along the roadway to cut a grooved path up to several feet wide and up to one-half inch deep.
The cutting of the roadway, which is typically cement or asphalt, generates tremendous amounts of frictional heat. This heat must be dissipated in order to increase the useful life of the cutting blades. One standard cooling method is to spray large amounts of water over the blades and over the pavement. This reduces friction, absorbs heat and washes away the cut pavement particles, called swarf, from the path of the blades. Where large pavement grooving machines are used, the amount of cooling water required becomes quite significant and when mixed with the large amounts of swarf, the water and swarf mixture forms an extremely messy slurry over large portions of the roadway. This residue, which may have a mud or clay type of consistency, must be removed before the roadway can be placed in service.
In the past, attempts have been made to remove the water and swarf from the pavement with various vacuum devices which draw the slurry through a plurality of nozzles into a vacuum manifold. One particular arrangement which is still in use is known as a "drag bar" which is typically mounted around the periphery of a blade box which covers the cutting blades. The drag bar is usually formed with a rectangular frame having a downward facing U-shaped channel approximately one inch high and two or three inches wide. A vacuum source is connected to the channel through a series of nozzles which are spaced along the outer surface of the frame so that each nozzle communicates via a flexible hose with a central vacuum manifold. The vacuum manifold is in turn connected to a cyclone separator and a vacuum source.
Numerous problems have been experienced with the use of drag bars. A very common problem is the plugging of the nozzles and hoses which connect the drag bar with the vacuum source. Such nozzles and hoses are often of small diameter, about one or two inches, and thus easily blocked by the water and swarf mixture which usually has a viscous consistency. Moreover, the flexible hoses are prone to wear and require frequent replacement. Also prone to wear is the lower surface of the drag bar channel which is continually abraded as it is dragged over the pavement. As the channel wears, its performance suffers from unwanted vacuum leakage and thus requires frequent replacement or rebuilding.
Still another problem associated with drag bars is the sudden fluid contraction and/or expansion energy losses which arise at each interface or connection between the drag bar frame channel and the hose nozzles. These losses reduce the ability of the vacuum system to effectively pick up and remove water and swarf from the pavement. Other energy losses are incurred at each subsequent transition in the vacuum ducting where sudden fluid expansion or contraction losses further promote plugging and greatly reduce the vacuum system performance. While some drag bars are provided with constant acceleration-type nozzles in place of constant diameter pipe-type nozzles, sudden contraction and/or expansion losses are still incurred downstream of the nozzle. As a result, these drag bar systems are also prone to blockage.
Another major drawback of a drag bar system is that by design, the water and swarf is first decelerated by impact against a blade shroud called a blade-box which serves as a safety housing that covers the cutting blades. After impact with the blade-box, the water and swarf are allowed to settle to the cutting surface. The water and swarf slurry must then be reaccelerated upwards by a vacuum generated air flow as the drag bar passes over the slurry. This is a clear waste of energy.
Another swarf removal system, commonly called a "slinger tray" system uses the tangential acceleration affect of a rotary cutting blade which is partially submerged in a fluid medium to transport the fluid along with swarf into a catch basis. No vacuum system is used. The slinger tray system typically removes from thirty to fifty percent of the swarf from the pavement. A major problem associated with the slinger tray system is that most of the swarf is left on the ground. This condition accelerates blade wear as the blades must spin within a slurry of abrasive swarf. Another significant problem with this system is that the large and heavy swarf particles which are entrained in the slurry tend to settle out, accumulate and fill the catch basis trough. This eventually blocks the slurry flow path and renders the basin useless.
All of the known systems discussed above require a blade-box which functions independently of the swarf removal system, and those systems which use a vacuum pick up mechanism require a separate removal device which surrounds the blade-box and which requires many nozzles connected to a central collection system. A significant problem associated with multiple nozzle systems is that it is extremely difficult to maintain the same level of vacuum between one nozzle and the next. What usually happens in practice is that the nozzle or nozzles with the least resistance, that is, those which are picking up the least amount of slurry and swarf, will, by the inherent characteristic of a vacuum system, receive the bulk of the vacuum flow available to the system. This is obviously a significant drawback since those nozzles which require the greatest vacuum flow receive the least.
Still another problem associated with multiple nozzle systems is that by their design, certain lengths or areas of the drag bar and pick up assembly are left without any available vacuum, thereby creating an area for slurry and swarf to escape from the vacuum system and leaving large amounts of slurry on the pavement.
Another drawback of systems using drag bars is that these systems are generally difficult to inspect. That is, because of the geometric configuration of the drag bars and the limited space available for their installation, it is quite difficult for the operator to inspect the cutting shaft bearings, vacuum hoses, vacuum nozzles and the drag bar integrity when installed on pavement grooving machines.